This invention relates generally to gas insulated equipment, and more particularly to a wheel-mounted insulator for use in gas-insulated transmission lines.
Compressed gas-insulated transmission lines typically comprise a hollow, cylindrical outer sheath, an inner conductor disposed within, but spaced apart from, the outer sheath, a plurality of insulating spacers which support the conductor in the sheath, and a compressed gas such as sulfur hexafluoride or the like in the sheath to electrically insulate the conductor from the sheath.
One problem occurring in the use of gas-insulated transmission lines concerns the mobile conducting or semi-conducting particle. These particles can cause problems in that they may lower the dielectric strength of the insulating gas and may initiate flash-over and break-down of the gas as they travel between the outer sheath and the inner conductor. Trump, in U.S. Pat. No. 3,515,938, disclosed a means for deactivating and eliminating the deleterious effects of such conducting particles. In that patent, there is described the use of electrodes placed within the outer sheath to create low field regions which trap and deactivate the particles. However advantageous these particle traps may be, it is still desirable to minimize the generation of such contamination particles to the extent possible. Thus, for example, assembly of the transmission line at the manufacturing site typically occurs in stages which includes, finally, assembly in a "clean room". However, even utilizing such precautions, it is not possible to eliminate all sources of contamination particles. In particular, in a typical gas-insulated transmission line, the support insulators which space the inner conductor from the outer sheath must extend outwardly to the outer sheath to provide the necessary support. There is thus a location where the support insulator must come in contact with the outer sheath. During assembly of the transmission line, this contact point must slide along the outer sheath in order to enable the inner conductor, with its insulators, to be inserted within the outer sheath. During such insertion, the abrasion of the support insulators against the outer sheath may generate contamination particles. The prior art minimized such generation by utilizing polytetrafluoroethylene pads at the ends of the support insulators where the insulators contacted in the outer sheath to facilitate the insertion while minimizing the abrasive forces therebetween. However, even utilizing such means, contamination particles were still generated. As another example, to provide for thermal expansion and contraction, the support insulators are not fixedly secured to the outer sheath but are allowed to slide relative thereto during actual use of the transmission line. During such expansion or contraction, the sliding of the support insulators against the outer sheath can also generate contamination particles. Thus, it is desirable to provide some means for minimizing the abrasive forces between the support insulators and the outer sheath to minimize the generation of contamination particles.